The invention relates to a method and apparatus for detecting trace amounts of explosives in soils and, more particularly, for detecting explosive-indicating compounds and munitions in near-surface soils.
Most methods for analyzing and detecting explosives or organic compounds that are indicative of the presence of explosives in subsurface soil require obtaining a soil sample, removing the soil sample to another location, extracting the organic compounds and analyzing the extracted supernatant with a standard chemical diagnostic technique to determine if explosive compounds are present. These methods have been generally designed to detect the presence of explosives for environmental remediation with sensitivities generally greater than approximately one part per million. Problems in reliable detection can occur when a soil sample is removed from its subsurface, in situ environment and transported to another location for subsequent processing steps wherein the explosive compounds are separated from the soil and then analyzed. Although steps can be taken to address these problems, the. compounds to be detected in the soil are subject to degradation, volatilization and contamination between the step of sampling and subsequent analysis at a separate location. Additionally, concentrations of the explosive compounds can be diluted below the sensitivity of the detection analysis equipment.
In order to detect buried landmines and unexploded ordnance (UXO), the detection apparatus must have a sensitivity significantly less than one part per million (Phelan, J. and Webb, S., Sandia National Laboratories report no., SAND97-1426, Sandia National Laboratories, Albuquerque, N.Mex., 1997). This is because the explosive compounds are generally not directly exposed to the soil but are contained within the landmine or UXO and diffuse out slowly. Additionally, it is useful to have a field portable apparatus and method that is mobile and functional in situ (below the soil surface) to provide rapid classification of explosive compounds, landmines, and UXO.
The U.S. Environmental Protection Agency (EPA) has developed a method for analyzing soils for explosive compounds. EPA Method 8330 describes a method for analysis of concentration of explosive residues in a water, soil or sediment matrix using high performance liquid chromatography. Soil samples are removed from their environment and generally transported to another location for analysis. Aqueous samples are diluted with methanol, filtered, and separated on a standard column. Soil and sediment samples are first extracted using acetonitrile in an ultrasonic bath and then analyzed similarly to the aqueous samples. The separation of the explosive compounds from the soil sample therefore occurs after the soil sample has been removed from its environment, thereby providing the opportunity for contamination, degradation and volatilization and thereby false readings. For the explosive residue chemical compounds of interest, such as trinitrotoluene (TNT), dinitrotoluene (DNT), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), the sensitivity in field contaminated soils is only approximately 1 to approximately 900 parts per million by weight.
Walsh and Jenkins (Marianne Walsh and Thomas Jenkins, U.S. Army Corp of Engineers, Special Report 91-7, June 1991) describe a method for field screening of one common explosive compound, referred to as hexhydro-1,3,5-trinitro-1,3,5-triazine (RDX), found in soils. In this method, similar to one developed for trinitrotoluene (TNT), a mild solvent and Greiss color reagent is added to a soil sample to produce a color change and specific absorbance when the explosive compound of interest is present. The method is utilized for RDX concentrations of approximately 1 part per million or higher.
Sausa (U.S. Pat. No. 5,759,859, issued on Jun. 2, 1998) describes a cone penetrometer apparatus for continuously measuring the concentration of energetic materials, such as explosive compounds, in potentially-contaminated soils using two lasers, one for decomposing an energetic material into NO (nitrogen oxide) fragments and the other to detect the NO. Although this is an in situ method for detecting NO, the sensitivity of the method is not provided. The method does not directly detect explosive compounds such as TNT, DNT, RDX, and HMX but merely the NO compound from the thermal fragmentation process, which could also be a thermal fragmentation by-product from other chemicals, such as fertilizers. The apparatus utilizes a truck to house the sensor components as well as a hydraulic press that is used to pull and push the penetrometer in or out of the ground.
Pomeroy (U.S. Pat. No. 4,641,566, issued on Feb. 10, 1987) describes an indirect method for detecting buried landmines where an area of interest is sprayed with a leach of ionized metal that is assumed to concentrate on an impervious object such as rocks or an impervious landmine. An array of detectors is then used to detect the enhanced concentration of ionized metal. Difficulties may arise in determining whether landmines are present when impervious objects such as rocks or man-made objects other than landmines are present in the subsurface or when the hydrological characteristics of the soil prevent uniform transport of the leach.
Useful for the detection of explosive compounds, landmines and UXO would be a method and apparatus for rapid analysis of soil in the subsurface soil and to detect explosive compounds originally contained in landmines or UXO or explosive chemical compounds indicative of the presence of explosives, landmines or UXO.
According to the present invention, an apparatus for detecting explosive-indicating compounds in soil is provided, comprising a sampling means for exposing an adsorbent material to soil, said adsorbent material capable of adsorbing at least one explosive-indicating compound, a means for desorbing said explosive-indicating compounds, and a diagnostic means for detecting said explosive-indicating compounds. The sampling means comprises an outer sheath and an inner probe, wherein the inner probe can be exposed to soil and wherein at least some portion of the surface of the inner probe is covered with the adsorbent material.
The desorbing means can be a solvent or a heating means, such as radiative heating, an inductive electrical circuit, a resistive electrical circuit, or a hot gas. The diagnostic means comprises at least one chemical detector. The chemical detector can be a mass detector, such as a mass spectrometer, acoustic wave device or quartz crystal microbalance; an optical-based detector, such as an infrared detector, an ultraviolet-visible detector, a refractive index detector, a fluorescence detector, a chemiluminescence detector or a Raman detector; a charged-mass detector, such as a magnetic sector analyzer, a time of flight analyzer, a quadrupole mass filter or an ion trap/ion resonance mass filter; a thermal conductivity detector, an electron capture detector, an immunoassay detector; or any chemical detector common to those skilled in the art in detecting organic chemicals. The diagnostic means can include both a chemical detector as well as a separations means, such as commonly present in chromatographic diagnostic instruments. The diagnostic means can be at least one diagnostic tool selected from a group consisting of an ion-mobility spectrometer, a gas chromatograph, a high performance liquid chromatograph, a capillary electrophoresis chromatograph, a mass spectrometer, a Fourier-transform infrared spectrometer, a Raman spectrometer or combination thereof.
The apparatus can be a field-portable instrument wherein the sampling means is connected to the diagnostic means or the sampling means can be unconnected from the diagnostic means and the sampling means transported to the location of the diagnostic means for analysis.
A method for detecting explosive-indicating compounds in soil is also part of the present invention, wherein a sampling means with an adsorbent material on at least some portion of a surface of the sampling means is inserted into the soil to contact the adsorbent material with the soil. The explosive-indicating compounds are then desorbed and transferred as either a liquid or gas sample to a diagnostic tool for analysis. An aqueous solvent can be added to the volume around the adsorbent material to enhance transfer of the explosive-indicating compounds in the soil to the adsorbent material. The explosive-indicating compounds are desorbed from the adsorbent material by a solvent or by heating. The resulting gas or liquid sample is analyzed by a diagnostic means. The diagnostic means comprises at least one chemical detector. The chemical detector can be a mass detector, such as a mass spectrometer, acoustic wave device or quartz crystal microbalance; an optical-based detector, such as a infrared detector, an ultraviolet-visible detector, a refractive index detector, a fluorescence detector, a chemiluminescence detector or a Raman detector; a charged-mass detector, such as a magnetic sector analyzer, a time of flight analyzer, a quadrupole mass filter or an ion trap/ion resonance mass filter; a thermal conductivity detector, an electron capture detector, an immunoassay detector; or any chemical detector common to those skilled in the art in detecting organic chemicals. The diagnostic means can include both a chemical detector as well as a separations means, such as commonly present in chromatographic diagnostic instruments. The diagnostic means can be selected from the group consisting of an ion-mobility spectrometer, a gas chromatograph, a high performance liquid chromatograph, a capillary electrophoresis chromatograph, a mass spectrometer, a Fourier-transform infrared spectrometer, and a Raman spectrometer to detect the presence of explosive-indicating compounds.